Gross-to-Net Salary Calculator documentation

Overview

The Gross-to-Net Salary Calculator computes net pay, every employee deduction and every employer contribution from a gross salary, using each country's official payroll algorithm. It also works backwards (net → gross) and runs up to 8 scenarios side by side.

Coverage today:

• Germany, tax years 2025 and 2026. Wage tax (Lohnsteuer) from our own implementation of the BMF Programmablaufplan (PAP): tax classes I–VI, child allowances, the factor procedure for class IV, an annual tax allowance from the tax card and age relief. Solidarity surcharge, church tax (8 % in Bayern and Baden-Württemberg, 9 % elsewhere), health insurance with the fund's add-on rate, long-term care with the childless surcharge, the child discounts and the Saxony split, pension and unemployment insurance with the contribution ceilings, and the employer's shares plus the insolvency levy.
• United Kingdom, tax years 2025-26 and 2026-27. PAYE income tax for any tax code (L, K, BR, D0–D3, NT, 0T, week 1/month 1, and the cumulative basis with pay and tax to date), Scottish (S) and Welsh (C) rates, and Class 1 National Insurance for categories A, B, C, H, J, M, V and Z, including the employer's NICs.
• Planned, not available yet: Austria, Switzerland, the Netherlands and the United States (federal + FICA). GET /countries lists them with "status": "planned".

What you get on top of a single net figure:

• Every deduction and contribution is its own line with payer (employee or employer), rate, base, the rule applied in words and the official source.
• employer_cost (gross plus employer contributions), deduction_rate and the figures scaled to a year (annual).
• profile echoes the profile as applied, including defaults the API filled in, and notes lists every assumption and what is not included.

How accurate is it? The German wage-tax engine matches 320 of 320 labelled cases generated from the BMF's own wage-tax calculator interface (160 per year: wage tax, solidarity surcharge, church-tax base, one-off payments). The UK engine matches all 336 PAYE rows and all 896 National Insurance rows of HMRC's software developers payroll test data for 2025-26 and 2026-27. That is 1,552 of 1,552 official cases to the cent. German social insurance has no official test oracle, so it is covered by hand-checked unit tests. The current numbers are shown on https://syntropicapi.com/apis/salary-net.

What it is not. Results are estimates for offers, budgeting and comparisons, not a payroll run and not tax advice. Special cases that the API does not model are rejected with a clear 400 error instead of being approximated: German Minijob/Midijob pay (up to 2,000 EUR per month), private health insurance (PKV) and employees above the statutory retirement age; for the UK, student loans and pensions are not deducted (the response says so in notes).

Base URL: https://syntropicapi.com/v1/salary-net. OpenAPI spec: https://syntropicapi.com/openapi/salary-net.json.

Amounts are in EUR for Germany and GBP for the UK. The API does not convert currencies.

Authentication

API key (syntropicapi.com). Buy credits at https://syntropicapi.com/pricing and send the key in the X-API-Key header (Authorization: Bearer <key> also works). Each successful call costs 1 credit, including a /compare call with 8 scenarios. Failed calls (4xx/5xx) are not charged. Successful responses carry an X-Credits-Remaining header.

curl -s "https://syntropicapi.com/v1/salary-net/countries" -H "X-API-Key: $SYNTROPIC_API_KEY"

RapidAPI. Subscribe to the API on RapidAPI and call it with your RapidAPI key (X-RapidAPI-Key and X-RapidAPI-Host headers, as shown in the RapidAPI code snippets). Your RapidAPI plan sets the quota. You don't need a syntropicapi.com key.

MCP (AI agents). The same five operations are MCP tools at https://syntropicapi.com/mcp/salary-net/mcp (Streamable HTTP). Send your syntropicapi.com key in the X-API-Key header. Each tool call costs 1 credit. Listing the tools is free. The tools are calculate_net_salary, calculate_gross_salary, compare_net_salaries, get_payroll_parameters and list_salary_countries, and their arguments are the same as the REST bodies and parameters below. For example, with Claude Code:

claude mcp add --transport http salary-net https://syntropicapi.com/mcp/salary-net/mcp --header "X-API-Key: $SYNTROPIC_API_KEY"

x402 pay-per-call is not enabled on this deployment at the moment (https://syntropicapi.com/health reports "x402": false). Use an API key, RapidAPI or MCP.

Request body: scenario and profiles

POST /net, POST /gross and each entry of POST /compare share these fields:

Sending the other country's profile is a 400 error ("The uk profile is not used for DE; send a de profile instead."). Unknown fields are rejected.

German profile (de)

UK profile (uk)

Response fields (/net and /gross): country, year, tax_year (2026 or 2026-27), period, currency, gross, net, employee_deductions, employer_contributions, employer_cost, deduction_rate (employee deductions in % of gross), annual (gross, net, employer_cost × periods per year), lines, profile, notes, sources (name, url, license) and disclaimer.

Each entry in lines has key (income_tax, solidarity_surcharge, church_tax, health_insurance, care_insurance, pension_insurance, unemployment_insurance, insolvency_levy, national_insurance), label, amount, payer, rate (in %, where a single rate applies), base, rule and source. A contribution that both sides pay appears twice, once per payer. On the UK cumulative basis amount can be negative (a tax refund).

For annual, a year has 12 months, 52 weeks, 26 fortnights, 13 four-week periods or 360 days.

Endpoints

POST /net

Gross → net for one pay period, with every deduction, the employer cost and the sources.

Example: Germany 2026, 4,500 EUR per month, tax class I, Bavaria, church member

curl -s -X POST "https://syntropicapi.com/v1/salary-net/net" -H "X-API-Key: $SYNTROPIC_API_KEY" -H "Content-Type: application/json" -d '{"country": "DE", "year": 2026, "gross": 4500, "period": "month", "de": {"tax_class": 1, "state": "BY", "church": true}}'

Response (trimmed: source shortened, the employer's pension and unemployment lines and the sources list left out):

{
  "country": "DE",
  "year": 2026,
  "tax_year": "2026",
  "period": "month",
  "currency": "EUR",
  "gross": 4500.0,
  "net": 2819.08,
  "employee_deductions": 1680.92,
  "employer_contributions": 958.5,
  "employer_cost": 5458.5,
  "deduction_rate": 37.35,
  "annual": {"gross": 54000.0, "net": 33828.96, "employer_cost": 65502.0},
  "lines": [
    {"key": "income_tax", "label": "Lohnsteuer (wage tax)", "amount": 650.16, "payer": "employee", "rate": null, "base": null, "rule": "PAP 2026: tax class 1, 0 child allowances, pay period month", "source": "BMF: Programmablaufplan für die maschinelle Berechnung der Lohnsteuer 2026 (BMF-Schreiben)"},
    {"key": "solidarity_surcharge", "label": "Solidaritätszuschlag", "amount": 0.0, "payer": "employee", "rate": null, "base": null, "rule": "PAP: 5.5 % of the wage tax with child allowances, zero below the exemption limit and phased in above it", "source": "BMF: Programmablaufplan … 2026"},
    {"key": "church_tax", "label": "Kirchensteuer", "amount": 52.01, "payer": "employee", "rate": 8.0, "base": 650.16, "rule": "8 % (Bayern) of the church-tax base 650.16 EUR (wage tax with child allowances, PAP output BK)", "source": "Kirchensteuergesetze der Länder: 8 % in Bayern and Baden-Württemberg, 9 % in the other Länder"},
    {"key": "health_insurance", "label": "Krankenversicherung (health)", "amount": 393.75, "payer": "employee", "rate": 8.75, "base": 4500.0, "rule": "14.6 % general rate + 2.9 % add-on, split equally", "source": "Sozialversicherungs-Rechengrößenverordnung 2026"},
    {"key": "health_insurance", "label": "Krankenversicherung (health)", "amount": 393.75, "payer": "employer", "rate": 8.75, "base": 4500.0, "rule": "14.6 % general rate + 2.9 % add-on, split equally", "source": "Sozialversicherungs-Rechengrößenverordnung 2026"},
    {"key": "care_insurance", "label": "Pflegeversicherung (long-term care)", "amount": 108.0, "payer": "employee", "rate": 2.4, "base": 4500.0, "rule": "3.6 % total; +0.6 % childless surcharge paid by the employee (age 23+, no children)", "source": "Sozialversicherungs-Rechengrößenverordnung 2026"},
    {"key": "care_insurance", "label": "Pflegeversicherung (long-term care)", "amount": 81.0, "payer": "employer", "rate": 1.8, "base": 4500.0, "rule": "3.6 % total; +0.6 % childless surcharge paid by the employee (age 23+, no children)", "source": "Sozialversicherungs-Rechengrößenverordnung 2026"},
    {"key": "pension_insurance", "label": "Rentenversicherung (pension)", "amount": 418.5, "payer": "employee", "rate": 9.3, "base": 4500.0, "rule": "18.6 %, split equally", "source": "Sozialversicherungs-Rechengrößenverordnung 2026"},
    {"key": "unemployment_insurance", "label": "Arbeitslosenversicherung (unemployment)", "amount": 58.5, "payer": "employee", "rate": 1.3, "base": 4500.0, "rule": "2.6 %, split equally", "source": "Sozialversicherungs-Rechengrößenverordnung 2026"},
    {"key": "insolvency_levy", "label": "Insolvenzgeldumlage (insolvency levy)", "amount": 6.75, "payer": "employer", "rate": 0.15, "base": 4500.0, "rule": "Employer-only levy on pay up to the pension ceiling", "source": "SGB V § 241/§ 242 (health), SGB XI § 55 (care), SGB VI § 158 (pension), SGB III § 341 (unemployment)"}
  ],
  "profile": {"tax_class": 1, "state": "BY", "church": true, "children": 0, "child_allowances": 0.0, "parent": false, "childless_surcharge": true, "health_insurance_addon_rate": 2.9, "birth_year": null, "factor": null, "annual_tax_allowance": 0},
  "notes": [
    "Health insurance add-on rate (Zusatzbeitrag) not given; used the official average of 2.9 % for 2026. Each fund sets its own rate.",
    "Employer cost excludes the fund-specific U1/U2 levies and statutory accident insurance (BG), which depend on the employer's health fund and industry."
  ],
  "sources": ["…"],
  "disclaimer": "Estimate for offers, budgeting and comparisons, not a payroll run and not tax advice. Computed with the official algorithms and the rates cited on each line; individual circumstances (other income, benefits in kind, pensions, fund-specific levies) can change the result."
}

Example: UK 2026-27, 55,000 GBP per year, Scottish taxpayer

No tax code given, so the API uses S1257L and says so in notes.

curl -s -X POST "https://syntropicapi.com/v1/salary-net/net" -H "X-API-Key: $SYNTROPIC_API_KEY" -H "Content-Type: application/json" -d '{"country": "UK", "year": 2026, "gross": 55000, "period": "year", "uk": {"region": "scotland"}}'

Response (trimmed: sources left out):

{
  "country": "UK",
  "year": 2026,
  "tax_year": "2026-27",
  "period": "year",
  "currency": "GBP",
  "gross": 55000.0,
  "net": 40811.13,
  "employee_deductions": 14188.87,
  "employer_contributions": 7500.0,
  "employer_cost": 62500.0,
  "deduction_rate": 25.8,
  "annual": {"gross": 55000.0, "net": 40811.13, "employer_cost": 62500.0},
  "lines": [
    {"key": "income_tax", "label": "Income tax (PAYE)", "amount": 11078.27, "payer": "employee", "rate": null, "base": 42421.0, "rule": "Tax code S1257L, scotland rates, week1/month1 basis; taxable pay to date 42,421 GBP", "source": "Scottish income tax rates and bands (Scottish Rate Resolution)"},
    {"key": "national_insurance", "label": "National Insurance (Class 1 employee)", "amount": 3110.6, "payer": "employee", "rate": null, "base": 55000.0, "rule": "Category A (Standard rate): 8 % between PT 12570 and UEL 50270 GBP per year, 2 % above", "source": "HMRC: Class 1 National Insurance thresholds, rates and category letters"},
    {"key": "national_insurance", "label": "National Insurance (Class 1 employer)", "amount": 7500.0, "payer": "employer", "rate": 15.0, "base": 55000.0, "rule": "15 % above the secondary threshold 5000 GBP per year", "source": "HMRC: Class 1 National Insurance thresholds, rates and category letters"}
  ],
  "profile": {"region": "scotland", "tax_code": "S1257L", "ni_category": "A", "basis": "week1/month1", "period_number": null, "tax_to_date": null},
  "notes": [
    "No tax code given; used the standard personal allowance code S1257L (personal allowance 12,570 GBP).",
    "Annual figures: tax on the annual basis, NICs with the annual earnings-period thresholds.",
    "Not included: pension auto-enrolment, salary sacrifice, student and postgraduate loans, and the Apprenticeship Levy (only for pay bills above 3 million GBP)."
  ],
  "sources": ["…"],
  "disclaimer": "Estimate for offers, budgeting and comparisons, not a payroll run and not tax advice. …"
}

Example: UK cumulative basis (month 6 with pay and tax to date)

Pass period_number, previous_pay and previous_tax to get the tax that PAYE deducts in that month, as payroll software does. Here the pay to date was high, so month 6 catches up.

curl -s -X POST "https://syntropicapi.com/v1/salary-net/net" -H "X-API-Key: $SYNTROPIC_API_KEY" -H "Content-Type: application/json" -d '{"country": "UK", "year": 2026, "gross": 4000, "period": "month", "uk": {"tax_code": "1257L", "period_number": 6, "previous_pay": 20000, "previous_tax": 2400}}'

Response (trimmed):

{
  "tax_year": "2026-27",
  "period": "month",
  "gross": 4000.0,
  "net": 2621.84,
  "employee_deductions": 1378.16,
  "employer_cost": 4537.45,
  "lines": [
    {"key": "income_tax", "label": "Income tax (PAYE)", "amount": 1142.0, "payer": "employee", "base": 17710.0, "rule": "Tax code 1257L, rest-of-uk rates, cumulative basis, period 6; taxable pay to date 17,710 GBP"},
    {"key": "national_insurance", "label": "National Insurance (Class 1 employee)", "amount": 236.16, "payer": "employee", "rule": "Category A (Standard rate): 8 % between PT 1048 and UEL 4189 GBP per month, 2 % above"},
    {"key": "national_insurance", "label": "National Insurance (Class 1 employer)", "amount": 537.45, "payer": "employer", "rate": 15.0, "rule": "15 % above the secondary threshold 417 GBP per month"}
  ],
  "profile": {"region": "england", "tax_code": "1257L", "ni_category": "A", "basis": "cumulative", "period_number": 6, "tax_to_date": 3542.0}
}

POST /gross

Net → gross: finds the smallest gross pay, to the cent, whose net pay reaches net, by bisection over the same engine as /net. The response has all /net fields for that gross pay plus target_net and difference (net - target_net, 0 when the target is reachable to the cent). Body: the scenario fields above with net instead of gross.

If the target needs a German gross in the Minijob/Midijob range (up to 2,000 EUR per month), the API returns 400 unsupported_profile.

Example: 3,000 EUR net per month in Hesse, tax class III, two children

curl -s -X POST "https://syntropicapi.com/v1/salary-net/gross" -H "X-API-Key: $SYNTROPIC_API_KEY" -H "Content-Type: application/json" -d '{"country": "DE", "year": 2026, "net": 3000, "period": "month", "de": {"tax_class": 3, "children": 2, "state": "HE"}}'

Response (trimmed: employer lines, notes and sources left out):

{
  "country": "DE",
  "tax_year": "2026",
  "period": "month",
  "currency": "EUR",
  "gross": 4077.33,
  "net": 3000.0,
  "employee_deductions": 1077.33,
  "employer_contributions": 868.46,
  "employer_cost": 4945.79,
  "deduction_rate": 26.42,
  "annual": {"gross": 48927.96, "net": 36000.0, "employer_cost": 59349.48},
  "lines": [
    {"key": "income_tax", "label": "Lohnsteuer (wage tax)", "amount": 225.16, "payer": "employee", "rule": "PAP 2026: tax class 3, 2 child allowances, pay period month"},
    {"key": "solidarity_surcharge", "label": "Solidaritätszuschlag", "amount": 0.0, "payer": "employee"},
    {"key": "health_insurance", "label": "Krankenversicherung (health)", "amount": 356.77, "payer": "employee", "rate": 8.75, "base": 4077.33},
    {"key": "care_insurance", "label": "Pflegeversicherung (long-term care)", "amount": 63.2, "payer": "employee", "rate": 1.55, "base": 4077.33, "rule": "3.6 % total; -0.25 % employee discount for 2 children under 25 (0.25 % from the 2nd to the 5th child)"},
    {"key": "pension_insurance", "label": "Rentenversicherung (pension)", "amount": 379.19, "payer": "employee", "rate": 9.3, "base": 4077.33},
    {"key": "unemployment_insurance", "label": "Arbeitslosenversicherung (unemployment)", "amount": 53.01, "payer": "employee", "rate": 1.3, "base": 4077.33}
  ],
  "profile": {"tax_class": 3, "state": "HE", "church": false, "children": 2, "child_allowances": 2.0, "parent": true, "childless_surcharge": false, "health_insurance_addon_rate": 2.9},
  "target_net": 3000.0,
  "difference": 0.0
}

POST /compare

Runs 1 to 8 gross-to-net scenarios (countries, years, profiles) and returns them side by side. One call costs 1 credit, whatever the number of scenarios. Amounts stay in each country's currency (no FX conversion); deduction_rate compares directly.

Each row has label, country, tax_year, currency, period, gross, net, employee_deductions, employer_cost, deduction_rate, annual_net, income_tax (income or wage tax plus solidarity surcharge and church tax) and social_contributions (employee social insurance or National Insurance). If one scenario is invalid, the whole call returns 400 with the scenario number, e.g. "scenario 2: …".

Example: 60,000 EUR in Germany (2026 and 2025) against 52,000 GBP in the UK

curl -s -X POST "https://syntropicapi.com/v1/salary-net/compare" -H "X-API-Key: $SYNTROPIC_API_KEY" -H "Content-Type: application/json" -d '{"scenarios": [{"country": "DE", "year": 2026, "gross": 60000, "period": "year"}, {"country": "UK", "year": 2026, "gross": 52000, "period": "year"}, {"country": "DE", "year": 2025, "gross": 60000, "period": "year"}]}'

{
  "rows": [
    {"label": "DE 2026, tax class 1", "country": "DE", "tax_year": "2026", "currency": "EUR", "period": "year", "gross": 60000.0, "net": 37561.0, "employee_deductions": 22439.0, "employer_cost": 72780.0, "deduction_rate": 37.4, "annual_net": 37561.0, "income_tax": 9389.0, "social_contributions": 13050.0},
    {"label": "UK 2026-27, 1257L", "country": "UK", "tax_year": "2026-27", "currency": "GBP", "period": "year", "gross": 52000.0, "net": 40721.0, "employee_deductions": 11279.0, "employer_cost": 59050.0, "deduction_rate": 21.69, "annual_net": 40721.0, "income_tax": 8228.4, "social_contributions": 3050.6},
    {"label": "DE 2025, tax class 1", "country": "DE", "tax_year": "2025", "currency": "EUR", "period": "year", "gross": 60000.0, "net": 37509.0, "employee_deductions": 22491.0, "employer_cost": 72660.0, "deduction_rate": 37.49, "annual_net": 37509.0, "income_tax": 9561.0, "social_contributions": 12930.0}
  ],
  "notes": ["Amounts are in each country's currency; convert with your own FX rate before comparing absolute values. deduction_rate compares directly."],
  "disclaimer": "Estimate for offers, budgeting and comparisons, not a payroll run and not tax advice. …"
}

GET /parameters

The allowances, tax bands, contribution rates and ceilings the engine uses for one country and tax year, each with its official source.

Each entry in parameters has key, label, value, unit and source.

curl -s "https://syntropicapi.com/v1/salary-net/parameters?country=DE&year=2026" -H "X-API-Key: $SYNTROPIC_API_KEY"

Response (trimmed: 8 of 21 parameters shown, source shortened):

{
  "country": "DE",
  "year": 2026,
  "tax_year": "2026",
  "currency": "EUR",
  "parameters": [
    {"key": "basic_allowance", "label": "Grundfreibetrag (basic tax-free allowance)", "value": 12348.0, "unit": "EUR/year", "source": "BMF: Programmablaufplan für die maschinelle Berechnung der Lohnsteuer 2026 (BMF-Schreiben)"},
    {"key": "child_allowance", "label": "Kinderfreibetrag incl. BEA per child (both parents)", "value": 9756.0, "unit": "EUR/year", "source": "BMF: Programmablaufplan … 2026"},
    {"key": "solidarity_exemption", "label": "Solidarity surcharge exemption limit (single; doubled in class III)", "value": 20350.0, "unit": "EUR tax/year", "source": "BMF: Programmablaufplan … 2026"},
    {"key": "bbg_kv_pv", "label": "Contribution ceiling health and care insurance", "value": 69750.0, "unit": "EUR/year", "source": "Sozialversicherungs-Rechengrößenverordnung 2026"},
    {"key": "bbg_rv_av", "label": "Contribution ceiling pension and unemployment insurance", "value": 101400.0, "unit": "EUR/year", "source": "Sozialversicherungs-Rechengrößenverordnung 2026"},
    {"key": "kv_addon_average", "label": "Average health insurance add-on rate (durchschnittlicher Zusatzbeitrag)", "value": 2.9, "unit": "%", "source": "SGB V § 241/§ 242 (health), …"},
    {"key": "pv_childless", "label": "Care insurance childless surcharge (employee)", "value": 0.6, "unit": "%", "source": "SGB V § 241/§ 242 (health), …"},
    {"key": "midijob_upper_month", "label": "Upper limit of the transition zone (Midijob)", "value": 2000.0, "unit": "EUR/month", "source": "SGB V § 241/§ 242 (health), …"}
  ]
}

For the UK (country=UK&year=2026) the list holds the personal allowance (12,570 GBP), the income tax bands for the rest of the UK, Wales and Scotland (e.g. "scotland: 42 % on taxable pay 31,093–62,430"), the NI lower earnings limit, primary and secondary thresholds and upper earnings limit per week, month and year, and the employee (8 %, 2 % above the UEL, 1.85 % for category B) and employer (15 %) NI rates.

GET /countries

Coverage: which countries and tax years are available, which pay periods and profile fields each accepts, the official test data each engine is checked against, and which countries are planned. No parameters.

curl -s "https://syntropicapi.com/v1/salary-net/countries" -H "X-API-Key: $SYNTROPIC_API_KEY"

Response (trimmed: two of the four planned countries shown):

{
  "countries": [
    {"country": "DE", "name": "Germany", "status": "available", "currency": "EUR", "years": [2025, 2026], "periods": ["year", "month", "week", "day"], "profile_fields": ["tax_class", "state", "church", "children", "child_allowances", "parent", "birth_year", "health_insurance", "health_insurance_addon_rate", "factor", "annual_tax_allowance"], "conformance": "BMF wage-tax calculator interface (labelled cases for the PAP of each year)"},
    {"country": "UK", "name": "United Kingdom", "status": "available", "currency": "GBP", "years": [2025, 2026], "periods": ["year", "month", "week", "fortnight", "four_weeks"], "profile_fields": ["region", "tax_code", "ni_category", "period_number", "previous_pay", "previous_tax"], "conformance": "HMRC software developers payroll test data (PAYE and Class 1 NICs), every row"},
    {"country": "AT", "name": "Austria", "status": "planned", "currency": "EUR", "years": [], "periods": [], "profile_fields": [], "conformance": "BMF Brutto-Netto-Rechner cases"},
    {"country": "US", "name": "United States (federal + FICA)", "status": "planned", "currency": "USD", "years": [], "periods": [], "profile_fields": [], "conformance": "IRS Publication 15-T worked examples"}
  ]
}

Errors and limits

Errors are JSON with a detail field. Failed calls are not charged.

Limits:

• gross up to 10,000,000 and net up to 5,000,000 per period.
• /compare: 1–8 scenarios per call.
• DE: gross pay above 2,000 EUR per month (or the equivalent for other periods), statutory health insurance, employees below the statutory retirement age.
• UK: period_number up to the number of periods in the year (12 for monthly pay, 52 for weekly pay). Student loans, postgraduate loans, pensions, salary sacrifice and the Apprenticeship Levy are not deducted.
• Employer cost for DE excludes the U1/U2 levies and statutory accident insurance (they depend on the employer's health fund and industry).
• Quotas: a syntropicapi.com key is limited by its credits. On RapidAPI, your plan's quota applies.

Data sources, freshness and update policy

Ground truth for the published accuracy numbers:

• Germany: labelled cases from the BMF's wage-tax calculator interface, which the BMF provides for program testing. They were generated offline; the interface is never called at runtime.
• UK: every row of HMRC's software developers payroll test data (PAYE and NICs), run through POST /net exactly as a customer would call it.

The rules and rates are built into the API, so responses are fast and deterministic and never depend on a third-party service. Every line names its source, and GET /parameters shows every value in use.

Update policy: each tax year is added as a new version and older years stay callable, so you can compare years and recalculate back pay. Germany changes every January (the BMF publishes the next year's PAP each autumn), the UK every April (HMRC publishes new test data before the tax year starts). New years are checked against the official test data before release, and the accuracy numbers on the API page are updated with them. Changes during a year (for example a new PAP mid-year) are applied when they are published.

Changelog

Every change to this API is listed in its public, signed and timestamped dev log: https://syntropicapi.com/apis/salary-net/devlog